Subtitles are uploaded as simple text based formats and can be created using a simple text editor. In most cases though, it will be more efficient and less error prone to use software designed for this purpose. Screen9 does not provide such software but we can give you recommendations on what software to use. Please note though that we do not provide support for this software and neither do we give any guarantees about its functioning.
Here's a short list of software which creates subtitles: